Merge pull request #91 from cellos51/hblank_affine_background_effects

HBlank based visual effects for affine background

include/affine_background.h

@@ -5,6 +5,7 @@
 
 #include "graphic_utils.h"
 
+#define AFFINE_BG_IDX 2 // The index of the affine background BGCNT register etc.
 #define AFFINE_BG_PAL_LEN 16
 #define AFFINE_BG_PB (PAL_ROW_LEN * 10) // This isn't really a palette bank, just the starting index of the palette
 
@@ -15,7 +16,8 @@ enum AffineBackgroundID
 };
 
 void affine_background_init();
-void affine_background_update();
+IWRAM_CODE void affine_background_hblank();
+IWRAM_CODE void affine_background_update();
 void affine_background_set_color(COLOR color);
 // Must be called with an array of size at least  AFFINE_BG_PAL_LEN
 void affine_background_load_palette(const u16 *src);

source/affine_background.c

@@ -4,49 +4,88 @@
 
 #include "graphic_utils.h"
 
-BG_AFFINE bgaff;
+#define ANIMATION_SPEED_DIVISOR 16
+
+BG_AFFINE bgaff_arr[SCREEN_HEIGHT + 1];
+
 AFF_SRC_EX asx = {0};
 
 enum AffineBackgroundID background = AFFINE_BG_MAIN_MENU;
 
+static uint timer = 0;
+
 void affine_background_init()
 {   
     affine_background_update();
 
-    bgaff = bg_aff_default;
+    REG_BG_AFFINE[AFFINE_BG_IDX] = bg_aff_default;
+}
+
+// Pre-computes the affine matrices values for each scanline 
+// and stores in bgaff_arr. 
+// This is to be done in VBLANK so the HBLANK code 
+// can just fetch the values quickly.
+IWRAM_CODE void affine_background_prep_bgaff_arr()
+{
+    for (u16 vcount = 0; vcount < SCREEN_HEIGHT; vcount++)
+    {
+        const s32 timer_s32 = timer << 8;
+        const s32 vcount_s32 = vcount << 8;
+        const s16 vcount_s16 = vcount;
+        const s32 vcount_sine = lu_sin(vcount_s32 + timer_s32 / ANIMATION_SPEED_DIVISOR); // dividing the timer by 16 to make the animation slower
+        
+        asx.scr_x = (SCREEN_WIDTH / 2); // 128 on x and y is an offset used to center the rotation
+        asx.scr_y = vcount_s16 - (SCREEN_HEIGHT / 2); // scr_y must equal vcount otherwise the background will have no vertical difference
+        asx.tex_x = (1000 * 1000) + (vcount_sine);
+        asx.tex_y = (1000 * 1000);
+        asx.sx = 128;
+        asx.sy = 128;
+        asx.alpha = vcount_sine + (timer_s32 / ANIMATION_SPEED_DIVISOR);
+
+        bg_rotscale_ex(&bgaff_arr[vcount], &asx);
+    }
+
+    /* HBLANK occurs after the scanline so REG_VCOUNT represents the 
+     * the scanline that just passed, so when it's SCREEN_HEIGHT we will
+     * actually be updating the first line
+     */
+    bgaff_arr[SCREEN_HEIGHT] = bgaff_arr[0];
+}
+
+IWRAM_CODE void affine_background_hblank()
+{
+    vu16 vcount = REG_VCOUNT;
+
+    if ((vcount >= SCREEN_HEIGHT)) // Exit the function if the scanline is outside the screen
+    {
+        return;
+    }
+
+    // See comment in affine_background_prep_bgaff_arr()
+    REG_BG_AFFINE[AFFINE_BG_IDX] = bgaff_arr[vcount + 1];
 }
 
 void affine_background_update()
 {
-    static uint timer = 0;
-    timer++;
-
-    switch (background)
+    if (REG_IE & IRQ_HBLANK) // High quality mode with HBLANK interrupt
+    {
+        affine_background_prep_bgaff_arr();
+    }
+    else // Low quality mode without HBLANK interrupt
     {
-    case AFFINE_BG_MAIN_MENU:
-        asx.scr_x = SCREEN_WIDTH / 2;
-        asx.scr_y = SCREEN_HEIGHT / 2;
-        asx.tex_x = 16560;
-        asx.tex_y = 14400;
-        asx.sx = 128;
-        asx.sy = 128;
-        asx.alpha = 1000; // This slightly rotates it which increases the perceived resolution of the background
-        break;
-    case AFFINE_BG_GAME:
         asx.scr_x = 0;
         asx.scr_y = 0;
         asx.tex_x += 5;
         asx.tex_y += 12;
-        asx.sx = (lu_sin(timer * 100)) >> 8; // Scale the sine value to fit in a s16
-        asx.sx += 256; // Add 256 to the sine value to make it positive
-        asx.sy = (lu_sin(timer * 100 + 0x4000)) >> 8; // Scale the sine value to fit in a s16
-        asx.sy += 256; // Add 256 to the sine value to make it positive
+        asx.sx = ((lu_sin(timer * 100)) >> 8) + 256; // Scale the sine value to fit in a s16
+        asx.sy = ((lu_sin(timer * 100 + 0x4000)) >> 8) + 256; // Scale the sine value to fit in a s16
         asx.alpha = 0;
-        break;
+
+        bg_rotscale_ex(&bgaff_arr[0], &asx);
+        REG_BG_AFFINE[AFFINE_BG_IDX] = bgaff_arr[0];
     }
 
-    bg_rotscale_ex(&bgaff, &asx);
-    REG_BG_AFFINE[2] = bgaff;
+    timer++;
 }
 
 void affine_background_set_color(COLOR color)
@@ -72,6 +111,7 @@ void affine_background_change_background(enum AffineBackgroundID new_bg)
     case AFFINE_BG_MAIN_MENU:
         REG_BG2CNT &= ~BG_AFF_32x32;
         REG_BG2CNT |= BG_AFF_16x16;
+        REG_IE |= IRQ_HBLANK; // Enable HBLANK
 
         memcpy32_tile8_with_palette_offset((u32*)&tile8_mem[AFFINE_BG_CBB], (const u32*)affine_main_menu_background_gfxTiles, affine_main_menu_background_gfxTilesLen/4, AFFINE_BG_PB);
         GRIT_CPY(&se_mem[AFFINE_BG_SBB], affine_main_menu_background_gfxMap);
@@ -80,6 +120,7 @@ void affine_background_change_background(enum AffineBackgroundID new_bg)
     case AFFINE_BG_GAME:
         REG_BG2CNT &= ~BG_AFF_16x16;
         REG_BG2CNT |= BG_AFF_32x32;
+        REG_IE &= ~IRQ_HBLANK; // Disable HBLANK
 
         memcpy32_tile8_with_palette_offset((u32*)&tile8_mem[AFFINE_BG_CBB], (const u32*)affine_background_gfxTiles, affine_background_gfxTilesLen/4, AFFINE_BG_PB);
         GRIT_CPY(&se_mem[AFFINE_BG_SBB], affine_background_gfxMap);

source/main.c

@@ -22,6 +22,7 @@ void init()
 {
     irq_init(NULL);
     irq_add(II_VBLANK, mmVBlank);
+    irq_add(II_HBLANK, affine_background_hblank);
 
     // Initialize text engine
     tte_init_se(0, BG_CBB(TTE_CBB) | BG_SBB(TTE_SBB), 0, CLR_WHITE, TTE_BIT_UNPACK_OFFSET, NULL, NULL);